Diffusion apparatus



Dec; 24, 1968 Filed May 51, 3.966

FIG.

G. KRIKORIAN DIFFUSION APPARATUS 2 Sheets-Sheet l 1968 G. KRIKORIAN 3, 5

DIFFUSION APPARATUS Filed May 31, 1966 2 Sheets-Sheet 2 FIG.Z

FIG-3 [-16.4

VII 4 2, z: 5 m *7 H INVENTOR GARO KRIKORIAN United States Patent 3,417,925 DIFFUSION APPARATUS Garo Krikorian, Paxton, Mass., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed May 31, 1966, Ser. No. 553,815 1 Claim. (Cl. 239-504) ABSTRACT OF THE DISCLOSURE A gas diffusion apparatus that includes a drum having a perforated outer wall, the perforations forming apertures in communication with a gas supply in the interior of the drum, and inserts positioned in each aperture. The inserts have a cylindrical base and integral therewith, a cylindrical upper member having a smaller radius than the base. The base engages the aperture wall and has a gas entry-office therein, communicating with a passageway extending axially through the base and into the upper member and terminating in an end wall. There is at least one side opening in the upper member located short of the end wall communicating with the passageway and being positioned with its longitudinal axis substantially perpendicular to the axis of the passageway.

This invention relates to a device for diffusing a gas jet. In particular, it relates to a device which permits a high-velocity, high-temperature gas jet to be diffused uniformly against the surface of a sheet material being treated with the gas.

It is well-known in the art to treat sheet materials such as paper, nonwoven fabrics, films and the like with hightemperature gas to effect drying, bonding or other physical or chemical treatments of the sheet material. In order for such treatments to be effective and uniform throughout the sheet, it is necessary for the entire sheet surface to be evenly contacted with the gas.

In the production of bonded nonwoven fabrics wherein the binder is activated by heating it at or above its softening or thermosetting point, it has been found that passing the gas through the sheet material will provide good contact and permit high production rates. In many cases, it is desirable to have the sheet material at least partially supported during the treatment, for example, by passing the material over the surface of a perforated drum, the interior of which is supplied with heated gas under pressure. In apparatus of this type, the perforations in the outside wall of the drum form apertures through which the gas is discharged against the material being treated. Because of structural limitations, there is a practical limit to the number of apertures which can be present in the outside wall of the drum. There is also a practical limit on the distance that can be tolerated between the exits of the apertures and the sheet material. Because of these practical considerations, perforated drums heretofore known have not provided adequate diffusion of the heated gas and accordingly uneven contact of the sheet material resulted, particularly with highvelocity, high-temperature gas was used to obtain the level of heat transfer required for high production rates. In bonding operations this can lead to over-bonding in some portions of the sheet and under-bonding in other portions.

The purpose of this invention is to provide a device for insertion into a cylindrical aperture to diffuse highvelocity gas flowing therethrough. Another purpose is to provide a device which, when used in apertures in the wall of a drum, will diffuse high-velocity air flowing through the apertures equally against the area of a sheet material being supported over the wall of the drum.

These and other purposes of the invention are attained by a device for diffusing gas, said device having a cylindrical base and integral therewith, a cylindrical upper member having a smaller radius than the base, said base having a gas-entry orifice therein communicating with a passageway defined by and extending axially through the base and into the upper member and terminating in an end wall, and at least one side opening in the upper member located short of the end Wall, communicating with the passageway and being positioned with its longitudinal axis substantially perpendicular to the axis of the passageway. The cylindrical base is adapted to be inserted into and frictionally engage the inner cylindrical surface of an aperture and the gas-entry orifice communicates with the means to supply gas to the aperture. The gas enters the passageway of the diffusing device and travels therethrough exiting at the side opening or openings at substantially a right angle to the passageway. The gas stream is thereby directed perpendicularly against the walls of the aperture and ultimately out of the aperture to evenly contact the sheet material that is being treated.

The invention will be further understood by reference to the drawings in which FIGURE 1 is a schematic side elevation of an apparatus for passing high-velocity gas through a sheet material while the material is being passed over and supported on perforated drums;

FIGURE 2 is a cross-section of a portion of a perfo' rated drum wall taken along line 22 of FIGURE 1;

FIGURE 3 is a cross-section of a diffusion insert taken along line 33 of FIGURE 2; and

FIGURE 4 is a plan view of a portion of the drum as in FIGURE 1 showing a strip Which supports a wire screen above the surface of the drum. The strip is wound helically around the surface of the drum.

Referring to FIGURE 1, sheet material 10 is fed into the nip between two porous belts 11 and 12, which are positioned and maintained under required tension in known manner by suitable rollers and guides. The two belts and the sheet material form a sandwich arrangement which is passed first over perforated drum 13 and then over perforated drum 14. The interiors of drums 13 and 14 are each provided with a supply of high-temperature air under pressure by means not shown. The insides of the drums act as plenum chambers and may be provided with taper cones so as to reduce progressively the volume of the plenum chambers as the air supply is diffused through the perforations or apertures 15. The drums are preferably equipped with distributors which confine the supply of gas to those portions of the drums which are contacted by the porous belts. The hot air passes from the interior of the drums, through the apertures and through the sandwich arrangement to achieve the desired heat treatment of the sheet material. The treated sheet material is separated from the porous belts at 16. By means of a suitable hood enclosure, not shown, the air is recirculated into the system by a blower fan, now shown.

In FIGURES Z and 3 one embodiment of the diffusing device 17 of this invention is shown positioned in apertures 15 of wall 18 of drum 14. The wall construction of drum 13 is similar and therefore is not shown. The apertures have a cylindrical portion 19 opening into the interior of the drum and a frusto-conical portion 21 opening at the exterior of the drum. The frusto-conical portions assist in providing better diffusion of the 'air and thereby improve contact of the air with the sheet material. Likewise the helically wound tape 22, which serves as a support for mounting wire screen 23 at a distance from the drum surface, provides an increased distance between the apertures and the sheet material and thus assists in providing even distribution of the air over the sheet Patented Dec. 24, 1968 material. Even with apertures having frusto-com'cal por tions and with the wire screen supported at a practical distance from the drum surface, however, the diffusion of the air is insufficient to heat the sheet material uniformly if the diffusing devices of this invention are not used.

The diffusion devices 17 of this invention comprise a cylindrical base 24, which secures the device in the cylindrical portion 19 of the aperture by means of an interference fit, and a cylindrical upper member 25 which is integral with and has a smaller radius than the base and hence a smaller radius than the cylindrical portion of the aperture. The axes of the base and upper member coincide. An orifice 26 in the base communicates with cylindrical passageway 27 which extends through the base and into the upper member Where it terminates as a blind end hole. Openings 28 communicating with the passageway are positioned in the upper member to divert gas perpendicularly to the wall of the aperture into the annular space between the upper member and the aperture wall. In the embodiment of the diffusing device in FIGURES 2 and 3, two openings into the passageway are shown. This is a preferred arrangement because the openings can be readily formed in a single drilling operation; but a single opening, or more than two openings can also be used, if

desired. It is essential, however, that the openings be positioned so that the gas is directed substantially at right angles to the walls of the aperture. If the gas flows in a direction having a radial component, that is, one parallel to the axis of the aperture, sufficient diffusion is not obtained. For example, a diffusing device having two openings in which the axes of the openings are at right angles to each other and each axis makes an angle of 45 with the axis of the aperture, is not acceptable because this arrangement does not provide even contact of the gas with the sheet material.

In a typical construction using the diffusion devices of this invention, perforated drums having an outer diameter of approximately 54 in. and a wall thickness of 1.25 in. are used. The perforations or apertures are located on 0.85 in. centers in a pattern as shown in FIGURE 4. The cylindrical portion of each aperture has a diameter of 0.375 in. The frusto-conical portion has an included angle of 60 and a diameter of 0.787 in. at its opening on the outer surface of the drum. Helical winding 22 is applied as a 0.037 in. thick x 0.437 in. Wide tape, edge-rolled to an internal diameter of about 54 in. It is positioned in an appropriately l'ocated helical groove in the roll surface, the helical groove having a 0.5 in. pitch. The tape is tack welded every 6 in. The helical winding is ground down to a height of 0.312 in. above the surface of the roll and then a 16 x 16 mesh, stainless steel screen having 0.023 in. diameter wires, is placed on the helical winding.

The diffusing devices are machined so that the base member has a diameter of 0.002 to 0.004 in. larger than the diameter (0.375 inch) of the cylindrical portions of the aperture in the drum Wall. In a preferred embodiment the outer surface of the base is roughened so that the root diameter of the base is 0.010 to 0.012. in. smaller than the maximum diameter. This permits the devices to be readily inserted into the apertures in the drum wall while also assuring adequate frictional engagement so that additional attachment as by tackwelding is not required.

If desired, however, tackwelding may be employed to secure the device in the aperture particularly where adequate frictional engagement is not obtained. The diameter of the upper member of the diffuser device is 0.250 in. Smaller or slightly larger diameters may be used consistent With achieving adequate diffusion. The overall length of the diffuser device is 0.437 in. and the upper member is 0.312 in. long. Cylindrical passageway 27 has a diameter of 0.187 in. and the openings in the upper member into the passageway likewise have a diameter of 0.187 in. The orifice in the base communicating with the cylindrical passageway may have a frusto-conical or countersunk design as shown.

An apparatus of the type described above is used to effect bonding of a nonwoven Web composed of randomly and uniformly disposed continuous filaments, of which are polyethylene terephthalate and 15% of which are an 80/20 copolymer of polyethylene terephthalate/ polyethylene isophthalate, the copolyester serving as the binder. Uniform bonding is obtained throughout the sheet as evidenced by the small variations in tear and tensile strength of samples taken throughout the bonded sheet.

In order to obtain acceptable release of the bonded nonwoven sheets, as described above, from the porous belts used to carry the web over the perforated drums, a coating such as a polysiloxane, polytetrafluoroethylene or fluorocarbon telomer is used on the belts. A preferred material of this type is the fluorocarbon telomer which can advantageously be applied as a dispersion in highboiling to 220 C.) fluid such as a fluorinated alcohol or ester. These dispersions form coherent coatings when applied to surfaces preheated to 150 to 240 C. without requiring a subsequent curing or fusing operation.

What is claimed is:

1. In a drum whose outside wall is perforated thereby forming a plurality of apertures each having a cylindrical portion communicating with the interior of the drum, the improvement comprising a device for diffusing gas located in each aperture, said device having a cylindrical base and integral therewith, a cylindrical upper member having a smaller radius than the base, said base being frictionally engaged with the inner cylindrical surface of the aperture, said base having a gas-entry orifice therein communicating with the interior of the drum and with a passageway defined by and extending axially through the base and into the upper member and terminating in an end wall, and said upper member having at least one side opening located short of the end wall and communicating with the passageway, said opening being positioned with its longitudinal axis substantially perpendicular to the axis of the passageway.

References Cited UNITED STATES PATENTS 2,917,241 12/1959 Waldrum ,239-222 2,978,187 4/1961 Hesson 239499 3,172,607 3/1965 Rivli et al 239499 3,313,002 4/1967 Wyeth 18-40 EVERETT W. KIRBY, Primary Examiner.

US. Cl. X.R.

186, 10; 29. s0.3; 1ss 22; l1860, 202; 239 -553.5, 590.5, 214 

